Field of the Invention
The present invention relates to headphones, specifically relates to a headphone that facilitates adjustment of sound quality in a low-frequency range without impairing the sound quality in all frequency ranges.
Description of the Related Art
FIG. 3 illustrates a sectional view of conventional sealed-type headphones disclosed in a patent document, such as Japanese Patent No. 5253072 B2. In FIG. 3, a baffle plate 2 is fit in an open end portion of a dish-shaped housing 20, and a driver unit 3 is fit into an opening formed in the baffle plate 2. As is well-known, the driver unit 3 has nearly the same configuration as a speaker unit. That is, although not illustrated, the driver unit 3 includes a magnetic circuit portion including such as a yoke, a magnet, a pole piece; a diaphragm; and a voice coil fixed to the diaphragm and disposed in a magnetic gap formed in the magnetic circuit portion.
A front side of the driver unit 3 is a surface on which the diaphragm is disposed (the lower side in FIG. 3). The housing 20 covers and seals a back side of the baffle plate 2 and a back side of the driver unit 3. A back cavity 4 having an appropriate volume is formed between an inner surface of the housing 20 and a plane defined by the back surfaces of the baffle plate 2 and the driver unit 3.
Further, a ring-shaped ear pad 5 is fixed to an outer periphery on a front side of the baffle plate 2. A space surrounded by the ear pad 5 forms a front cavity 6. When a user wears the headphones, the ear pad 5 is pressed against the side of the head of the user, and an ear of the user is accommodated in the front cavity 6.
Further, in the sealed-type headphones illustrated in FIG. 3, an acoustic resistance material 7 is attached in the back cavity 4 to mainly perform adjustment of sound quality in a low-frequency range. Further, it is also effective to cover a hole 8 formed in the baffle plate 2, which allows the back cavity 4 and the front cavity 6 to communicate with each other, with a damping material, that is, an acoustic resistance material having a high acoustic resistance, as illustrated in FIG. 3.
By the way, in the conventional headphones illustrated in FIG. 3, sound waves having a reverse phase emitted to the back side of the driver unit 3 (back cavity 4) flow to the front cavity 6 passing through the hole 8 for allowing the back cavity 4 and the front cavity 6 to communicate with each other.
However, since the hole 8 is disposed close to the ear pad 5, most of the sound waves having passed through the hole 8 from the back cavity 4 flow to the front cavity 6 through the ear pad 5. Therefore, there is a problem in that low-frequency sound waves cannot sufficiently pass to the front cavity 6 and a low-frequency component fails to be effectively cancelled at the front cavity 6, and resultantly the sound quality in the low-frequency range is deteriorated.